goldfish turning black

[tjacksonpfc]

Hi all thread title says it all. We have a tropical fishtank set up. Friends of ours were moving house 2 weeks ago and didnt want to put there sons goldfish through the stress of the move. Its a 6 hour drive away.

Dp said they could put him in our tank with our fish he has been really happy in there loads more room than hes used to. Hasn't been bothered or bothered the other fish.

However the dcs asked today why he is turning black and sure enough he has not got black sripes coming on his body from top to botttom. He is still feeding and swiming around quite happily. Any ideas from the fish experts out there. Would be much appreciated.

[EauRouge]

Sounds like it could be ammonia burns. Goldfish grow very large and need massive tanks, much bigger than most people think. You can't keep them alongside tropical fish, they need cooler water (which has a higher oxygen level) and there is a chance that they will eat any small fish you might have.

It could be that by adding it to the tank you have overloaded your filter and there has been an ammonia spike- have you tested the water since you added the goldfish.

It's really kind of you to rehome the fish but it'll be bad for its long-term health to be kept in a tropical tank. If it's a common goldfish then it will be best off in a pond once the weather warms up. Fancy goldfish need to be kept indoors and need a minimum tank size of around 30 gallons (135 litres) for one fish.